(Fox News) On a rainy afternoon last Spring, American pastor Eric Foley and his wife stood in a muddy field near the North Korea border and prayed – their hands clasped to a 40-foot homemade balloon that would carry Bibles to the communist dictatorship’s underground Christians.

“I get choked up, every time, as I let go and watch it take off,” Foley told FoxNews.com.

The balloons, made from a large sheet of “farm plastic,” said Foley, are filled with hydrogen before the Bibles and “tracts” – testimonials written by other North Korean Christians – are attached at the bottom inside a sack or box. Timers are then used to release the materials in stages, dispersing them at high altitudes across North Korea. Foley and members of his Christian mission group, Seoul USA, use GPS technology to help direct where the Bibles land. Around 50,000 of them have dropped from the skies in the last year.